Cameras and image sensors are in widespread use for surveillance, motion control and other applications. WDR sensors are becoming popular for automotive and surveillance applications to preserve the full dynamic range of a natural scene. Automotive applications, for example, include rear view cameras for assisting a driver while backing up, and cameras providing inputs to control systems for avoiding obstacles and controlling braking, steering, and acceleration.
Some next generation photodetectors provide a WDR output and are thus considered WDR image sensors. When a photographed image, such as from WDR image sensors, includes some of its pixels with bright regions and some other pixels with dark regions due to significant differences in the illumination intensity of the scene, an image of the scene clearly showing features in both the bright regions and dark regions cannot be obtained even when the exposure time and the aperture are properly adjusted. High dynamic range (HDR) imaging is an imaging technique that combines pixels from multiple frames (or exposures) having different exposure times, apertures, shutter speed and/or sensitivity) of the same picture (scene) with some pixels from each frame being used to encompass the brightness range of the entire frame set, generally so that the obtained picture covers the same dynamic range a human's eyes would. WDR imaging is a term used in the surveillance camera industry to refer to HDR imaging, where as used herein WDR imaging also refers to HDR imaging.
In conventional WDR imaging, image processing of raw pixel data (image pre-processing) is the first processing step, followed by a WDR merge (or fusion) algorithm, and then tone mapping. The input raw pixel data from the WDR sensor can be in the form of Bayer, RCCC, RGBC, or more generally in any 2×2 color format. The image pre-processing includes applying multiple algorithms including defective pixel correction (DPC), lens shading correction (LSC), noise filtering (NF), WDR processing, white balance (WB) and statistics collection. Statistics collection comprises statistics for all frames used, such as statistics for a long exposure time frame, a short exposure time frame, and a shortest exposure time frame. The raw pixel data can come directly from a WDR sensor (e.g., color camera) or from a memory (e.g. a double data rate synchronous dynamic random-access memory (SDRAM DDR).
WDR fusion of the pixel data follows the image pre-processing. Tone mapping that follows WDR fusion is for reducing the dynamic range (i.e., less bits), or contrast ratio, of the full color image while retaining localized contrast to provide a tone mapped image. A demosaicing (or de-mosaicing) algorithm which is a digital image process that reconstructs a full color image generally follows the tone mapping.